Estimating of Net Transition Probabilities in Triple Stages of Cigarette Consumption in Iranian Men.

Background
The present study was designed to estimate the net transition probabilities in triple stages of cigarette consumption in Iranian men over 15 years old.


Materials and Methods
Data from the national surveillance of risk factors of non-communicable diseases in 2011 were entered in the present study. Data of 3130 Iranian men between the ages of 15 and 69 years old were included. Individuals were divided to three groups of current smoker, past smoker and nonsmoker based on cigarette consumption. Afterwards, net transition probability of different stages of cigarette consumption over a year was assessed.


Results
Net transition probability from nonsmoker to smoker was at its highest level until 30 years of age at 19.1 per 1000 men and then net transition reduces to reach zero per 1000 men at the age of 45 years old. However, net transition probability from smoker to nonsmoker was at a very low level until 45 years of age but, it increases afterwards to reach a plateau at the age of 64 years old. Net transition probability from smoker to nonsmoker is estimated to be 23.1 per 1000 men at the age of 69 years old.


Conclusion
For the first time, the present study has estimated the transition probabilities in different stages of cigarette consumption in Iranian adults. Findings showed that risk of becoming a smoker in younger individuals is much higher than the risk in middle-aged and old population. However, tendency to quit smoking is increased after the age of 45 years old. Therefore, health policy makers should concentrate on younger age groups in their preventive strategies regarding control of tobacco consumption.


INTRODUCTION
Assessing the transition of individuals between different groups of cigarette consumption in a time period is defined as transition probability which has a great importance in health policy making systems (1). With the help of the mentioned concept, it can be predicted that how many nonsmokers will become smoker and how many will quit smoking in the following year or longer time periods.
Future cigarette consumption status of the country can be acknowledged based on mentioned estimations and such measures will help health policy makers in application of preventive strategies (2,3).
Cigarette smoking is considered the most important preventable risk factor of death across the world. Cigarette smoking is the risk factor of many diseases such as cancer, cardiovascular diseases, pulmonary fibrosis, and many other non-communicable diseases (4)(5)(6)(7). Relative risk of getting a cancer is 23 times greater in smokers compared to nonsmokers (4,6). Cigarette smoking is responsible for the death of more than half of its long-term consumers as almost 5 million adults lost their lives due to cigarette smoking in 2000 (about 12% of all deaths in 2000) and this amount is estimated to reach 8.3 million individuals in 2030. Seventy percent of these deaths occurred in developing countries (4).
World Health Organization (WHO) estimates that there are 1.3 billion smokers across the world consisting one third of population over 15 years old which will ultimately reach 2 billion people if the mentioned pattern of cigarette smoking remains until 2030 (8). Cigarette smoking prevalence in Iran is reported to be about 19% in men and 1.5% in women with a total prevalence of 11.9% in Tehran and 12.5% across the country (9, 10).
Cigarette consumption is divided into three stages in an epidemiological view including current smokers, past smokers and nonsmokers. Individuals who have smoked at least 100 cigarettes either daily or occasionally are considered current smokers. Individuals who were used to smoke in a daily manner and have quitted are considered past smoker and individuals who have not smoked a cigarette are considered nonsmokers (1).
Although there are many studies across the world assessing cigarette smoking and its different consumption stages (1,(11)(12)(13)(14)(15), there are no studies assessing net transition probability in different stages of cigarette consumption in Iranian adults. Hence, the goal of the present study was to estimate the net transition probabilities in triple stages of cigarette consumption in Iranian men using data from the national surveillance of risk factors of non-communicable diseases in 2011.

Variables
Data cleaning was performed before analysis of gathered data. Data cleaning needs to be highly accurate and its correct application leads us to more reliable results.
Hence, the accuracy of entering data and amount of missing were assessed. The way of entering data was the first source of error. The mentioned error which is a common problem in large databases was assessed. Therefore, frequency of data of each variable was obtained first and then minimum and maximum amounts of each column were assessed. This method gave us the opportunity to get a quick look at the data. In addition, both very high and very low amounts which could not be attributed to cigarette smoking were evaluated. At the end, the amount of missing data was specified. The amount of observed missing was less than 0.6% which could be ignored. Statistical analyses were done when accuracy of data was assured.
Cigarette consumption status (and its kinds) was assessed in Iranian men between 15 and 69 years old.
Variables of age, age at which first cigarette was smoked and age at which cigarette smoking was quitted were In the present study, movement of individuals between different stages of cigarette consumption within a year was defined as transition.

Statistical analyses
Data analysis was performed using R software.  Table 1 shows different stages of cigarette consumption based on age groups.    Table 2).In addition, analysis showed that some nonsmokers start smoking and then quit smoking until the age of 50 years old.
The mentioned probability reaches its maximum at the ages of 30 to 35 years old (5.9 to 6.2 individuals per 1000 people) and becomes almost zero after the age of 50 years old ( Figure 2 and Table 2).

DISCUSSION
The present study showed that net transition probability from nonsmoker to smoker reaches its maximum at the age  (17,19).

CONCLUSION
For the first time, the present study has estimated the transition probability in different stages of cigarette consumption in Iranian adults. The present study which has used data of the national surveillance of risk factors of noncommunicable diseases showed that probability of becoming a smoker reaches its maximum at the age of 30 years old and then net transition decreases to reach zero at almost the age of 45 years old. In addition, tendency to quit smoking is increased after the age of 45 years old compared to younger ages. Therefore, health policy makers should concentrate on younger age groups in their preventive strategies regarding control of tobacco consumption.